More on ICC Profiles, sRGB, and scRGB

The best way to understand the relationship between ICC profiles, sRBG, and scRGB is as complementary tools performing similar tasks under different conditions — the same way that a paring knife, a steak knife, and a bread knife are all cutting tools, with each one working best for a different kind of cutting. As such, it helps to know what each of these tools was designed for. The short form is that ICC Profiles are for professionals, sRGB for consumers, and scRGB for home-savvy ‘prosumers.’ But, of course, there’s a lot more to it than that.

Historically, professionals in such areas as graphic arts, photography, and prepress work have been the groups most concerned with color management in digital photos, graphics, and the like. Traditionally this has meant relying on closed-loop calibration — calibrating one specific piece of equipment with another — and on proprietary color management schemes that vary from one product to the next. If you were a photographer who dealt with two or more service bureaus, for example, you would have to maintain a separate closed-loop calibration for each service bureau. ICC profiles are meant to provide a standard approach to the professional’s color management needs.

The International Color Consortium (ICC) was formed in 1993 as the ColorSync Consortium, with Apple Computer as the driving force, and including Sun, SGI, Microsoft, Adobe, Agfa, and Kodak. The essential goal was to define a standard for color management. The route taken was, first, to define a profile connection space (PCS), which explicitly describes relevant parameters for describing colors. The PCS describes an idealized reflective print on a paper that is a perfect, non-selective diffuser, with colorants (Read: dyes or inks) that have a large dynamic range and color gamut. The viewing environment is a standard ANSI PH-2.30 viewing booth with a D50 illuminant — a daylight light source equivalent to a 5000 degree color temperature.

With the PCS defined, it first becomes possible to define a profile for each device in terms of that space. This profile connection space provides what you might think of as a common language for colors. The ICC profile for any given input or output device (camera, scanner, monitor, or printer) describes what the color information for that device means in terms of the profile connection space, and gives the transforms to and from that space.

By adding the profile information to an image file, the profile can also describe what the color information in that file means. And with the profile in hand, a program or operating system that supports ICC profiles can map the colors from one device to another. In short, the profile connection space effectively serves as the basis for universal translation of colors.

At least, that’s the essence of how ICC profiles work. But it’s important to understand that the reality of using ICC profiles is a bit messy. (You should also be aware that there are some limitations to ICC profiles. In particular, the PCS doesn’t define all the parameters it should ideally define, and some of the things that it does define are defined ambiguously. Most of these limitations are tangential to this discussion; they are discussed in articles on the ICC Web site, www.color.org, including the paper ICC Achievements and Challenges at www.color.org/iccach1.html.) However it is worth noting that because ICC profiles are less than perfect, many professionals and service bureaus, particularly those working with printed CMYK output as their final destination, prefer staying with the tried and true methods that predate ICC Profiles.

You’ll find support for ICC profiles in both Apple’s Macintosh operating systems (by way of ColorSync 2 and later) and in Microsoft Windows 98 and later (through ICM 2.0 image color matching; ICM 1.0 in Windows 95 also supported ICC profiles, but only in a limited way). But this operating system support doesn’t automatically give you color management. It merely opens the door to using ICC profiles.

Any given scanner, camera, monitor, or printer may or may not come with an ICC profile. Those that do may or may not install the profile automatically when you install the driver; if they don’t, it’s up to you to install it manually. For those that don’t come with an ICC profile, you may be able to find a profile on a Web site, which again you can install manually. (To install a profile in any version of Windows, you can right click on the profile, and choose Install Profile. This copies the file into the Windows/System/Color folder and adds the profile to the Registry. Then go to the Properties dialog box for that device, go to the Color Management Tab, and choose Add.)

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